Coppick



March 17, 1964 S. COPPICK MODIFIED AMINOPLAST RESIN FOAMS AND PROCESS3,125,621

OF MANUFACTURE THEREOF Filed Feb. 8, 1961 'CURED AMINOPLAST RESIN FOAMControlled Pressure Hem and Humidity.

COMPRESSED FOAM 90% REDUCTION IN VOLUME FOAM PRODUCT PERMANENTCOMPRESSION SET INVENTOR.

SYDNEY COPPICK mqmk AGENT 3,125,621 I MODIFIED AMINOPLAS'LRESW FOAMS ANDa PROCESS OF MANUFACTURE THEREOF Sydney Coppick, Ridley Park, Pa.,assignor to Scott Paper Company, Philadelphia, Pa., a corporation ofPennsylvania Filed Feb. 8, 1961, Ser. No. 87,743 Claims. (Cl. 264-321)The' present invention relates to foamed aminoplast resins and moreparticularly to a process of modifying such resin foams under controlledconditions of pressure and temperature in order that there may berealized products of superior physical characteristics and of enhancedvalue.

The past few years have seen an increased interest in the development offoamable synthetic resinous materials whose cellular structures offerconvenient and satisfactory substitutes for an unlimited variety ofnatural spongeous bodies. The foamed polystyrenes, polyurethanes,

' alkyds and reconstituted celluloses are well known to the art. Morerecently attention-has been directed to a class of aminoplast resinfoams, the production of which involves some unusual techniques. Forexample, a ureaformaldehyde prepolymer, formed by condensing urea andformaldehyde in an approximate 1 to 2 molar ratio, may be foamed byaddition to a cellulated mass of a surface active agent, water and anacid catalyst such as sulfuric acid. Regulation of the density of thecellulated matrix by aeration thereof enables control of the density ofthe resin foam within limits of from 0.2 to 0.8 pound per cubic foot.Additionally it has been noted that the degree of aeration and matrixagitation affects the fineness of the ultimate foam which may leave asmany as cells per cubic centimeter. Upon curing there results areticulated structure whose skeletal configuration is composed ofrod-like strands arranged in a three-dimensional network consisting oftwo continuous phases with unique geometry and having spacings betweenthe strands corresponding in spacial dimensions with a foamed cellularproduct of 10 cells per cc. Melamine-formaldehyde resins, mixedmelamine-ur -thiourea condensation prodnets with formaldehyde andphenol-formaldehyde resins may be similarly processed to producelightweight foams. Other foamed resins are disclosed in US. Patents Nos.2,076,295, 2,273,367, 2,384,387, 2,559,891 and 2,813,780, British PatentNo. 768,562, Italian Patent No. 590,887, Belgian Patents Nos. 527,694,565,130 and 580,849.

The foamed resins, described above, are notably nonabsorptive. Water,when applied to the foam surface collects in droplets thereon ratherthan wetting and penetrating the interior of the foam. Attempts havebeen made to render these foams more water absorbent by treatment withsurfactants of different types but such efforts have not achieved anyreal degree of success.

It is a primary object of the present invent-ion to provide a controlledprocess for the compression and thermal ,setting aminoplastresin foam inorder to obtain therefrom a hydrophilic felt-like sheet of modifiedsoftness and flexibility.

It is another object of my invention to provide for the selectivemodification of the physical characteristics of an aminoplast resin foamaccompanied by volume concentration in excess of 50%.

Other objects and advantages of this invention will be readily apparentfrom the following detailed description of certain preferred embodimentsthereof.

I have discovered that under carefully controlled conditions ofpressure, time and temperature a reticulated foam structure of anaminoplast resin, hydrophobic and non-wettable, can be converted into ahydrophilic wettable U at Patent 3,125,621 Patented Mar. 17, 1964 2spongi-form body. Additionally such physical treatment will impartfibrous characteristics to the foam body, transforming it into a soft,flexible felt-like sheet. Control of the conditions under which materialcompression is efiected are critical. Resin fusion and the formation ofa coalesced polymer skin or surface for the" foam body, even thoughbeneficial from the standpoint of integral reinforcement is to beavoided.

The invention is best understood by reference to the drawing wherein:

The area represented as Cured Aminoplast Resin Foam depicts the foamsubjected to processing steps needed to prepare the hydrophobic foam forconversion avoiding those undesirable ones.

to the permanently compressed hydrophilic state;

The area represented as Compressed Foam Reduction in Volume depicts thefoam which in its original form in convenient shapes such as slabs,blocks and sheets having a certain humidity (or moisture) content is fedbetween two felt-like surfaces at a temperature of less than 210 -F. toeffect according to the coacting conditions of temperature, humidity,and particular pressure surfaces'the desired reduction in volume of theoriginal foam shape;

The area represented by Foam Product Permanent Compression Set depictsthe final foam product exhibiting in the final form thedesiredproperties.

In the present invention the three-dimensional strand structure isuniformly collapsed by breaking, bending and permanent deformation ofthe strands so that they lie substantially in a plane at right angles tothe direction of the compressing force. To carry out this process mosteffectively I have discovered that a uniform temperature throughout themass of the structure is desirable to avoid a non-uniformity ofunder-compression and adverse geometry in the interior of the sheet, andover-plasticization of the surface, resulting in coalescense of strandswith consequent skin formation. Furthermore the time, temperature,pressure relationship has been discovered to be very important inbringing about the desirable effect while In the preferred embodiment ofthis invention it is essential to impart a permanent set into thestructural strand elements of the reticulated three-dimensionalstructure so that the strands may be permanently bent and otherwisedistorted into the plane of the resulting sheet, without reducing themto such a plastic or fluid state that they are fused together to give ahard boardy material or have sufficient surface fusion to form a skin orshell which will impede absorption. To this end I prefer to use highpressure and relatively low but uniform temperature of relatively longduration to insure uniform penetration. By such means the strands assumea distortable or very highly viscous character without approaching atacky state. To effect a permanent flow or non-returnable distortion inthe strands at the softened but highly viscous state it is necessary toapply pressure for appreciable time duration in the area in which theelastic limit has been exceeded and to allow for fixation of thestrained strands in their distorted state, since otherwise theirresidual resilient properties would tend toward a partial or completerecovery to the original state. On the other hand the permanentdistortion properties may be enhanced by proceeding to a more softenedor less viscous state where pressures for short durations of time willeffect a non-recoverable collapse of the structure. However, in theselatter cases the temperatures required are such that a tackiness of thestrands results and their points of contact in the sheet are fusedtogether with the resulting loss of softness, and the surfaces of thefelted sheet are fused to the extent that water penetration is 3 Thefollowing examples are illustrative of the invention: I

Example I Preparation of a labile aminoplast resin, particularly adaptedfor thermal compression setting, involved the condensation of 1,200par-ts by weight of urea, 1,165 parts of para formaldehyde, 2,206 partsof water, 190 partsof methanol, 104 parts of urotropin(hexamethylenetetramine) and parts of 4 molar sodium hydroxide solution.The reactants were placed in a reaction flask equipped with a refluxcondenser, a thermometer and a mechanical stirrer. The flask was heatedunder agitation to reflux temperature of about 98 -C. and containedunder reflux for minutes. Then 40 par-ts of 10% sodium hydroxidesolution were added to stop the reaction and the resulting syrup wascooled to room temperature. The product had a viscosity of 55centistokes at C.

To 52 parts of the above resin syrup there was added 1 part of urea, 5partsjo'f 34% Teepol 610(a sodium secondary alkyl sulfate'p'rjoduced byShell Chemical Corporation) and 42 parts of water. I

The diluted resin solution containing the surfactant and a hardeningagent in the form of a solution containing 7.5 parts of 85% phosphoricacid, 2.0 parts of urea and 90 parts of water were blended in a foamingnozzle by pumping the resin solution and the hardening agent into themixing zone in the proportion of 2 volumes of resin to 1 volume ofhardener. mitted to the mixture which proceeded at high velocities overa tortuous path containing obstacles to convert the resin into a finefoam. This was collected in wire mesh containers and placed in acirculating air curing oven, with air circulation rate of 1000 cubicfeet per minute for 3 hours at a temperature of 85 C. and 42% relativehumidity. A moist, cured, reticulated three-dimensional strand structurewas obtained. This was dried in the same oven at 5% relative humidityand 60 C. for an additional period of 4 hours. A moisture plasticizedstructure with a density of 0.5 pound per cubic foot was obtained,having a very fine strand structure.

This cured and dried reticulated structure composed of two continuousphases was cut on a band saw to give slabs 1" thick. These slabs wereplaced between blotters and fed to the Nobel and Wood dryer and heldbetween the dryer surface and the rotating felt for a single period ofone revolution with a duration of 2.25 minutes, with the watertemperature inside the drum at 200 F. The final product was a soft pad Athick. This pad had a density of 8.0 lbs./ft. or a bulk of 7.8 cc./ gm.

A 1 cc. portion of water was placed on the pad and the three time takenfor complete absorption.

Material: Absorbency (seconds) Compressed. felted pad 22. Originaluncompressed slab Greater than 7200.

Example II Compressed air was ad- 5 exception that the Nobel and Wooddrum temperature A pad was made as in Example with the exception ExampleIII l A pad was made as in Example I with the exception I that the Nobeland Wood drum dryer temperature was 210' F. Absorbency: 15 seconds.

Example IV A pad was made as in Example I with the dryer temperature at170 F.

Example VI 1 A reticulated structure was prepared as in Example I. Slabswith a thickness of A" were cut with a band saw and compressed for 2.25minutes on the Nobel and Wood dryer at a drum temperature of 120 F. Theresulting pad had the following properties:

Basic weight 25 lbs./reamof 2880 sq. ft. Caliper 17 thousandths of inch.Bulk 10.25 cc./ gm.

Density 6.1lbs./ft.

Absorbency (1 cc.) 70 seconds.

Example VII A pad was made exactly as in Example VI with the was F. Theresulting pad had the following prop-- erties:

perature at which the compression is accomplished has a large efiect onthe absorbency of the resulting pad.

I Example VIII Slabs were compressed on the Nobel and Wood dryer atvarious temperatures for various times. The results were as follows:

Original Slab Thickness (inches) 34 14 M 1 1 Temperature of Drum, F 195220 220 220 220 Time 0! Compression (min.)- 2.25 2.25 4. 5 2.25 4.5Final Caliper, Thousandth inch 22 25 26 73 Basic Weight, lbs/ream 40.244.2 40. 1 94.2 95. 7 Bulk, ocJgm 8. 3 8. 6 9. 8 11. 5 11. 5 Density,f/ft. 7. 6 7. 26 6. 67 6. 41 6.41 Absorbency (second) 17 17 33 28 It isapparent from the above example that under the preferred conditions ofthisinvention the duration of the compression is not critical.

Basic weight 93.6 lbs/ream of 2880 0. Example Caliper 45.0 thousandthsof aninch. 65 Slabs were compressed as in Example VTII with theAbsorbency of pad 25 seconds. exception that the blotters used containedvarious amounts Absorbency (control slab) Greater than 18,000 seconds.of moisture.

Original Slab Thickness,

inches 76 A u 7t it as A Temperature of Drum F 220 220 220 220 220 Time0! Compression mtn.)- 2.25 2 25 2.25 2.25 2.25 4.5 2.25 2.25 2.25Moisture Content of Blotters, 5 5 5 6 6 l 11 1 Ails orben (seconds) 6 85 8 8 15 4 Felt si 720 140 30 a0 22 75 25 240 Drum an 17 15 13 22 16480. 25 3,000

Example X slabs of reticulated structures similar to Example I werecompressed on the Nobel and Wood dryer for various periods. The resultswere as follows:

Temperature, F 220 220 220 Time (minutes) 2.25 10.0 30 Moisture content,percent 5 5 5 Absorbency (seconds):

Felt side 30 15 45 30 20 Dryer side It is further indicated in theseexamples that so long as the moisture content is low, the plasticity ofthe material is such that at these preferred temperatures, the residencetime is not critical in the softness and absorbency of the resultingpad.

It is apparent from the foregoing results that the soft ness andabsorbency of a foamed aminoplast resin are materially benefited by thecompression and thermal set contemplated by my invention. It is furtherapparent that there exists a wide range of combinations of operatingconditions such as degree of compression, foam tem perature duringcompression, humidity control, and the like which will enable attainmentof the desired modification of physical properties of the treated foam.

The compressed foam of our invention is not only softened and givenhydrophilic properties but is also strengthened through its conversioninto a form approximating a felted material adopted for use in surgicaldressings, catamenial pads, and absorbent fillers where compliance,resilience and hydrophilicity are most desirable characteristics.

What I claim is:

1. The process of improving the physical characteristics of a lowdensity labile, cured aminoplast resin foam which comprises exerting auniform compressive force against such foam to reduce the volume thereoffrom to and to exceed the elastic limit of the structural elements ofthe foam without material destruction, such compression being effectedat a temperature between and 210 F., maintaining the moisture content ofthe compressed foam below 10% by having a porous felt like material incontact with the external surfaces of said foam when said foam issubjected to pressure, and maintaining the compression of said foam fora period less than 5 minutes to achieve a permanent set of the foammaterial in its compressed state.

2. The process of claim 1 in which the aminoplast resin is aurea-formaldehyde resin.

3. The process of improving the softness and hydrophilicity of a lowdensity labile, cured aminoplast resin foam which comprises heating saidfoam to a temperature of from 125 to 210 F., exerting a uniform compressive force against said heated foam to reduce the volume thereoffrom 50 to 95% and to exceed the elastic limit of the structuralelements of the foam without material destruction, maintaining themoisture content of the compressed foam below 10% by having a porousfeltlike material in contact with the external surfaces of said foamwhen said foam is subjected to pressure and maintaining the compressionof said foam for at least 2 minutes to achieve a permanent set of thefoam material in its compressed state.

4. The process of claim 3 in which the aminoplast resin is aurea-formaldehyde resin.

5. A hydrophilic aminoplast resin foam produced by the process definedin claim 1.

References-Cited in the file of this patent UNITED STATES PATENTS2,384,387 Meyer Sept. 4, 1945

1. THE PROCESS OF IMPROVING THE PHYSICAL CHARACTERISTICS OF LOW DENSITYLABILE, CURED AMINOPLAST RESIN FOAM WHICH COMPRISES EXERTING A UNIFORMCOMPRESSIVE FORCE AGAINST SUCH FOAM TO REDUCE THE VOLUME THEREOF FROM 50TO 95% AND TO EXCED THE ELASTIC LIMIT OF THE STRUCTUREA ELEMENTS OF THEFOAM WITHOUT MATERIAL DESTRUCTION, SUCH COMPRESSION BEING EFFECTED AT ATEMPERATURE BETWEEN 125* AND 210*F., MAINTAINING THE MOISTURE CONTENT OFTHE COMPRESSED FOAM BELOW 10% BY HAVING A POROUS FELTLIKE MATERIAL INCONTACT WITH THE EXTERNAL SURFACES OF SAID FOAM WHEN SAID FOAM ISSUBJECTED TO PRESSURE, AND MAINTAINING THE COMPRESSION OF SAID FOAM FORA PERIOD LESS THAN 5 MINUTES TO ACHIEVE A PERMANENT SET OF THE FOAMMATERIAL IN ITS COMPRESSED STATE.